Apparatus with power source for plating

ABSTRACT

Apparatus and method for plating with a pulsating direct current variable in frequency so as to obtain desirable plating characteristics. The amplitude as well as the frequency of the plating current may be adjusted to obtain superior plating results.

United States Patent 3,475,312 10/1969 lnoue Inventor Johann KarlHausner Chicago, Ill.

Appl. No. 722,435

Filed Apr. 18, 1968 Patented Oct. 26, 1971 Assignee Nova-Chrome, Inc.

Chicago, Ill.

APPARATUS WITH POWER SOURCE FOR PLATING 5 Claims, 6 Drawing Figs.

U.S. Cl. 204/228, 204/D1G, 9, 204/51 Int. Cl 801k 3/00 Field of Search204/228, 45.9, 51,35, 224

References Cited UNITED STATES PATENTS 3,481,839 12/1969 Inoue w t/33X2,443,599 6/1948 Chester 204/228 2,515,192 7/1950 Chester 204/2282,706,170 4/1955 Marchese. 204/228 3,276,976 10/1966 .luliard 204/433,294,666 12/1966 Wiersma 204/228 FOREIGN PATENTS 446,112 1/1948 Canada204/45.9

Primary Examiner-John H. Mack Assistant Examiner-D. R. ValentineAttorney-Hill, Sherman, Meroni, Gross & Simpson ABSTRACT: Apparatus andmethod for plating with a pulsating direct current variable in'frequencyso as to obtain desirable plating characteristics. The amplitude as wellas the frequency of the plating current may be adjusted to obtainsuperior plating results.

APPARATUS WITH POWER SOURCE F OR PLATING BACKGROUND OF THE INVENTION 1.Field of the Invention The invention relates in general to plating, andin particular to a new and novel plating apparatus and method wherein analternating current is superimposed on a direct current applied to aplating bath and the amplitude and frequency of superimposed alternatingcurrent produces improved plating characteristics.

2. Description of the Prior Art My prior patent entitled Electroplating,U.S. Pat. No. 2,824,830 discloses superimposing on a DC field in aplating bath at least two high-frequency fields of relatively highfrequencies.

SUMMARY OF THE INVENTION An improved apparatus and method of platingwhich uses semiconductor devices for producing a direct current platingsignal upon which is superimposed alternating current pulses of varyingamplitudes and which may be varied in frequency and in time on and timeoff to control the shape of the AC pulses and obtain much improvedplating results over the prior art. An amplifier is provided which whenconnected in the circuit prevents feedback.

Other and further objects of this invention will be apparent to thoseskilled in this art from the following detailed description of theannexed sheets of drawings which, by way of a preferred embodiment ofthe invention, illustrate one example of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of theplating apparatus of this invention.

FIG. 2 is a graph of the plating response in which the AC signal has afrequency of 450 hertz.

FIG. 3 is a graph of the plating response using an AC pulse of 550hertz.

FIG. 4 illustrates a plating characteristic utilizing an AC pulse of 700hertz;

FIG. 5 illustrates a plating characteristic utilizing a 600 hertzsignal; and

FIG. 6 illustrates a plating response utilizing an AC signal of 1,800hertz.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 illustrates a platingbath 10 which includes a cathode II and an anode 12 to which platingleads I3 and 14 are attached, respectively. A cathode-ray oscilloscope16 connected across the leads I3 and 14 indicates to an operator thewave shape of the applied signal to the plating bath.

For example, plating may be carried out in a chrome plating aqueouselectrolyte bath, having 250 grams per liter of CrO, (as chromic acid),1.8 percent sulfuric acid (H 50 3 percent boric acid (H 80 and l percentoxalic acid. In this bath, the essential pH control is provided by thesulfuric acid, but superior results are obtained by the use also ofsubstantially 0.5-5.0 percent boric acid and 0.1-3.0 percent oxalicacid. (Unless otherwise specified, the terms parts and "percentage" meanthe same by weight). The plating bath is maintained at 135 F., whileplating with a cathode current density of about 2-3 amperes per squareinch. The anode may be lead or other conventional material. The specificcathode A.S.I. (DC) is measured when the pulsating current in operationis recited with other operating conditions in FIGS. 2 through 6, andunder the conditions established in such figures.

A resistor R, is also connected across leads I3 and 14. An ammeter I7 isconnected in line 13 and is bridged by a suitable shunt R, A diode D, isconnected to resistor R, and a condenser C, is connected from line I4 todiode D,. A voltmeter I8 is connected across condenser C,. A source of3-phase 220 volts, for example, AC is connected to terminals 19, 20 and21 and through a circuit breaker 22 to a Y primary 23 of a transformer.A light 24, for indicating that power is on, is connected betweencontacts 20 and 19 in series with a resistor R,. A delta-connectedportion of the transformer is designated as 24 and is connected toadjustable wiper contacts 26, 27 and 28 which engage the Yconnectedprimary 23 to vary the voltage to the unit 24 of the transformer. AY-connected output 29 is magnetically coupled to the portion 24 and isconnected to a full-wave rectifier designated generally as 31, and whichcomprises the diodes D, through D An inductor L, is connected betweenthe diodes D,, D, and D, and the diode D,. Thus the rectifier 31supplies rectified direct current to the plating bath. The inductor L,and capacitor C, provide a smoothing filter. Lead 32 is connected tolead I4 and provides an input lead for superimposing an AC pulsingsignal on the direct current supplied to the plating bath. A second lead33 provides the second lead for providing the AC pulsating input to theplating bath. A pair of input leads 34 and 36 are connected to asuitable AC source as, for example, l20-volt single-phase alternatingcurrent power. The circuit breaker 37 is connected in circuit with inputterminals 34 and 36. A resistor R and indicator light 38 are connectedacross the input terminals 34 and 36. Primary 39 of an auto transformeris connected to tenninals 34 and 36, and has a secondary 41 which has aslide contact that may be controlled by the knob 42. A secondary 43 iscoupled to the winding 41, and supplies an input to a rectifierdesignated generally as 44, comprising the diodes D, through D,,.Condenser C, is connected across the output terminals of the rectifier44. A variable potentiometer 46 is connected to point B and controls thetime off of the alternating current output. The potentiometer 46 isconnected to the base of a transistor T, which has its collectorconnected to the base of a transistor T The collector of transistor T,is connected to a tunnel diode D A time-on potentiometer 47 is connectedto the emitter of transistor l,. A pair of diodes D and D are connectedin series between the emitters of transistors T, and T,. A resistor R isconnected between the tunnel diode D and the base of a transistor T Theemitter of the transistor T is connected to the base of transistor T Thecollector of transistor T, is connected to the bases of transistors T,through T,,. A lead 48 is also connected to the potentiometer 46 and toresistors R through R,, which have their opposite sides connected to theemitters of the transistors T through T An input terminal for reversebias 49 is connected to lead 48 and a terminal SI is connected to thebases of the transistors T through T through the resistor R Lead 33 isconnected to the collectors of the transistors T, through T through aswitch 52. The switch 52 is closed when the solenoid 53 is energized. Abias voltage is supplied by rectifiers 54 and 56 which respectivelycomprise diodes D through D and diodes D,, through D The rectifier 54 isconnected across the secondary 57 of a transformer which has its primary58 connected to the power leads 34 and 36. A primary 59 of a transformeris also connected to the input power leads 34 and 36 and has itssecondary 61 connected to the rectifier 56. A resistor R is connected toone output of the rectifier 54 and condensers C,. C, and C are connectedin parallel between the other output lead of the rectifier 54 andresistor R A lead 62 is connected between the resistor R and point B ofthe rectifier 44. The time-on potentiometer is also connected to thecondensers C C and C,. A lead 63 is connected to the output of therectifiers 54 and $6 and a resistor R, is connected between the lead 63and the collector of the transistor T Lead 63 is also connected to theemitter of the transistor T,. A light 64 is connected across the outputof the rectifier 56. A resistor R is connected in series with a diode Din one output line of the rectifier 56 and a pair of condensers C, andC, are connected in parallel between the leads 66 and 67. A resistor Rand a variable resistor R and a resistor R and a capacitor C areconnected between the collector of transistor T, and lead 66. A resistorR is connected from resistor R, to a unijunction transistor UT, andparticularly to the base 1 terminal. The emitter tenninal of theunijunction UT, is connected to the junction point between the resistorR, and the capacitor C The base 2 electrode of the unijunctiontransistor UT, is connected to resistors R and R, which have theiropposite sides connected to the lead 66. A diode D is connected from thebase 2 of the unijunction transistor UT to a resistor R which has itsopposite side connected to resistor R and a resistor R which has itsopposite side connected to the lead 67. A capacitor C is connectedbetween resistor R and a resistor R which has its opposite sideconnected to the lead 67. An SCR is connected between capacitor C andlead 66 and has its control electrode connected to the base 2 of theunijunction transistor UT,. A second SCR, is connected between resistorR, and lead 66 and has its control electrode connected to the base 2electrode of a unijunction transistor UT, A resistor R is connectedbetween the control electrode of the SCR, and lead 66. A resistor R isconnected from resistor R to the first base electrode of the unijunctiontransistor UT,. Variable resistor R is connected in series with theresistor R between the resistor R and the emitter of the unijunctiontransistor UT,. The condenser C is connected between lead 66 andresistor R The solenoid 53 is connected across the output terminals ofthe rectifier 56.

In operation, power is applied to terminals 19, 20,21, 34 and 36, andthe potentiometers 46 and 47 are adjusted with knob 42 and contacts 26,27 and 28 to obtain an input to the electrodes 11 and 12 of the platingbath to obtain a greatly improved plating characteristic. The AC pulsesapplied by leads 32 and 33 to the bath are superimposed upon the directcurrent from the rectifier 31 and the frequency of the pulses may beadjusted as well as the on" and "05" duty cycle by controlling thepotentiometers 46 and 47, for example. The transistors T through T,operate as a pulse generator and a meter 70 is connected from lead 48 tolead 32 and indicates the amplitude of the pulses. The unijunctiontransistors UT, and U1, and SCRs, SCR, and SCR prevent feedback andprovide an improved output of the pulse generator.

FIGS. 2 through 6 illustrate the plating characteristics that may beobtained with different adjustments at the circuit of FIG. 1. FIG. 2,for example, illustrates the plating characteristic utilizing an outputAC pulse of 450 hertz with an amplitude of 7 volts and with the directcurrent voltage read by meter 18 being 5 volts, and the meter 17 reading3 amperes, and with the pulse current being equal to 1% amperes. It wasfound that the plating had a Rockwell hardness of C68, that the qualityof the plating was poor, that the throwing power was poor and that thebuildup was heavy, but that there were no bleeders. As shown in FIG. 2,the plating rate was relatively slow.

FIG. 3 illustrates the plating characteristic using a frequency outputof the pulse generator of 550 hertz with meter 70 reading 7 volts, themeter 18 reading 5 volts, and the DC current read by meter 17 being 3amperes, and the: pulse amperage being 1% amperes. The Rockwell hardnesswas C72; quality of the plating was excellent; throwing power wasexcellent, and there were no bleeders or buildup. It is to beparticularly noted that the plating rate was over twice as great as theplating which occurred under the conditions of FIG. 2. Specifically, in4 hours of plating, the characteristics of FIG. 2 resulted in athickness of 0.006 inch, whereas the characteristic of FIG. 3 resultedin a plating thickness of 0.0 14 inch.

FIG. 4 is a plating characteristic utilizing a pulse frequency of 700hertz at an amplitude of 6 volts and with a DC voltage being equal to 5volts and a DC amperage equal to 3 amperes, and the pulse amperage beingl'k. The Rockwell hardness for the plating was C70; the quality wasgood; the throwing power was good; there were no bleeders, and there wasonly slight buildup.

FIG. 5 illustrates a plating characteristic utilizing a pulse frequencyof 600 hertz at an amplitude of 5 volts, with the DC voltage being 6,the DC amperage being 3 and the pulse amperage being 1%. The Rockwellhardness was C72; the quality and throwing power were excellent, andthere were no bleeders or buildup. H

FIG. 6 illustrates a plating characteristic utilizing 1,800

hertz for the pulse frequency, with the amplitude equal to 5 volts. TheDC voltage was 5; pulse voltage was 3'6; DC amperage was 2 amperes, andthe pulse amperage was Hi. The Rockwell hardness was C70; the qualityand throwing power were fair; there were no bleeders, and there was onlyslight buildup.

It is seen that the characteristics illustrated in FIG. 3 give muchimproved results over the characteristics illustrated in the otherfigures-2, 4, 5 and 6. Thus, by controlling the amplitude of the pulsesand the frequency of the pulses, muchimproved plating results may beobtained. The pulse-on and pulse-off time controls the pulse current,and the conditions illustrated in FIG. 3 provide muchimproved platingresults.

It is interesting to note the plating speed variation as a function offrequency. Note that at 450 and 1,800 hertz, the plating thickness is0.006 of an inch after 4 hours; whereas at 550 hertz the plating reaches0.0l4 of an inch at 4 hours.

Although I have herein set forth my invention with respect to certainspecific principles and details thereof, it will be understood thatthese may be varied without departing from the spirit and scope of theinvention as set forth in the hereunto appended claims.

I claim as my invention:

1. In an electroplating apparatus having a plating bath and electrodes,an improved source of power comprising:

a source of direct current voltage attached to said electrodes.

an alternating current pulse generator producing a series of outputpulses which are superimposed on the output of the source of directcurrent voltage, means for adjusting the length of each output pulse asa function of time forming a part of said pulse generator, means foradjusting the time off of each of said output pulses independent of thelength of said pulses forming a part of said pulse generating, means foradjusting the amplitude of said output pulses forming a part of saidpulse generator, and means for adjusting the amplitude of the output ofsaid direct current source.

2. A source of power according to claim 1 wherein the ratio of the timeon to time off of the pulse generator varies from on ID percent of thetime to on percent of the time.

3. A source of power according to claim 1 wherein the frequency of saidpulse generator is between 500 to 700 hertz.

4. A source of power according to claim I where the frequency of saidpulse generator is in the vicinity of 550 hertz.

5. A source of power according to claim 1 including means for preventingfeedback in the pulse generator.

2. A source of power according to claim 1 wherein the ratio of the timeon to time off of the pulse generator varies from on 10 percent of thetime to on 80 percent of the time.
 3. A source of power according toclaim 1 wherein the frequency of said pulse generator is between 500 to700 hertz.
 4. A source of power according to claim 1 where the frequencyof said pulse generator is in the vicinity of 550 hertz.
 5. A source ofpower according to claim 1 including means for preventing feedback inthe pulse generator.